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A-8 Appendix PLZ-4W
A.2.4 Operation of the CV Mode
In CV mode, the PLZ-4W sinks current so that the voltage at the load input end of
the PLZ-4W is constant.
■
CV mode operation
When the PLZ-4W is used in CV mode, the PLZ-4W operates as a constant voltage
load (shunt regulator) as shown in Fig. A-9. When V1 is greater than V, the input
voltage V is kept constant even when the input current I varies. Current does not
flow when V1 is less than or equal to V.
In the Fig. A-9, R1 is the internal resistance of the constant-voltage power supply.
The PLZ-4W may operate unstably if R1 is low.
Fig. A-9 Equivalent circuit of the CV mode and operation
■
Transition of the operating point: Overpower protection (OPP)
We will consider the case when checking the load characteristics of the constant-
voltage power supply of Fig. A-9 using CV mode.
Fig. A-10 Transition of the operating point in CV mode (OPP trip point)
We assume that the overcurrent protection (OCP) setting I
OCP
is greater than current
I
N
at point N and denote the voltage of the constant voltage power supply as V
M
.
When the voltage of the PLZ-4W is equal to V
MO
(V
MO
> V
M
), no current flows.
When the voltage of the PLZ-4W is decreased to a point in which V
MO
is smaller
than V
M
, the current starts flowing. If the voltage is decreased further
(V
M1

V
M2

V
N
) to increase the input current (load current), the operating point
moves along segment MN (M
1

M
2

N).
0
PLZ-4W Series Electronic Load
Constant voltage
power supply
Current I
V
oltage V
I
V
R
1
Voltage is constant even
when the current varies
V
1
Input current [A]
Input voltage [V]
Log scale
V
M
V
M0
V
N
V
M2
V
M1
Constant power line
(OPP setting)
Constant voltage line
(Constant voltage setting)
Operating area
OPP trip point
M
N
I
N
I
OCP
M
1
M
2